1. Dynamic Planet 2005 Cairns, Australia 22-26 August 2005
Towards the Next Earth Gravitational Model to Degree 2160: Status and Progress
Dynamic Planet 2005
Cairns, Australia
22-26 August 2005
Steve Kenyon, John Factor, NGA
Nikolaos Pavlis, Jarir Saleh, Simon Holmes, Raytheon IS

2. Earth Gravitational Model 2006
CHAMP and GRACE satellite gravity missions
100x improvement in the accuracy with which large regional features of the gravitational field can be modeled
• Need for higher-resolution model of the gravitational field and geoid
5’ x 5’ resolution
n=m=2160
15 cm global RMS accuracy goal for geoid
Joint Navigation Conference Yes_____ No_____
CHAMP (Challenging Mini-Satellite Program) is a…
GRACE (Gravity Recovery and Climate Experiment) is a joint NASA/TBD program to measure the Earth’s gravitational field at wavelengths of TBD and larger with unprecedented accuracy. The improvements to the long wavelength promise improvements in determining the orbits of LEO satellites.
GOCE (?) is a
24 Aug 05

3. Progression of EGMs EGM96 EGM06 30’x30’ resolution 5’x5’ resolution
50 cm RMS accuracy
70 x 70 error propagation
40 satellites used for long ’s
30 M surface gravity values
29 elevation codes
130 K coefficients
EGM06
5’x5’ resolution
15 cm RMS accuracy
2160 x 2160 error propagation
CHAMP and GRACE used for long ’s
52 M surface gravity values
SRTM, ICESAT
4.7 M coefficients
24 Aug 05

4. 24 Aug 05

5. EGM06 Geoid Goals EGM06 Geoid Error Goal - 15 cm Global RMS
5 cm commission error from GRACE out to n=m=100
3 cm omission error beyond 2160 following Kaula's Rule
NGA’s detailed gravity data are expected to meet an ~14 cm geoid commission error requirement for degrees
24 Aug 05

6. EGM06 Geographic Accuracy Breakdown
Ocean areas with good altimetric data: from +/- 5 cm to +/- 10 cm
Land areas with good surface gravity data: from +/- 10 cm to +/- 15 cm
Land areas with poor surface gravity data: from +/- 15 cm to +/- 50 cm
Land areas with no surface gravity data: from +/- 50 cm to +/- 120 cm
24 Aug 05

7. Data Collection Methods
UNCLASSIFIED
Data Collection Methods
To satisfy the geodetic and geophysical (G&G) requirements of our DoD and IC customers, we have developed a broad range of data collection sources.
Some data can be acquired from orbital sensors, for example Global Positioning System, Shuttle Radar Topographic Mission and Satellite Altimetry ocean data.
For surface data, surveys are required. NGA is the depository of all DoD surveyed gravity data.
In addition, much of our information is obtained through informal data exchange with other organizations that have conducted surveys (oil and geophysical companies, universities and foreign agencies).
We do have some external assistance funds to support data acquisition in void areas. These funds are used to support field surveys or the cost of providing existing data to NGA.
We also partner with other organizations in the scientific community (like the International Association of Geodesy or Society of Exploration Geophysicists)
to acquire data.
24 Aug 05

8. 24 Aug 05

9. 24 Aug 05

10. Statistics of 5’x5’ g (v081005)
Source  Area Min. Max. RMS 
ArcGP
Altimetry
Terr. 15’
Fill-in
Actual 5’
All
(, ) , 293.5 , 204.5
The Fill-in anomalies for v have decreased
from 16.7 to 3.2  of the world compared to PGM2004A
24 Aug 05

11. Mongolian Aerogravity Project
24 Aug 05

12. JGP95E 5’x 5’ Global Elevation Source Codes
24 Aug 05

13. SRTM World Coverage Map
Coverage between latitudes 60 N - 54 S
80% of the Earth’s landmass
24 Aug 05

14. KINEMATIC GPS GROUND CONTROL POINT COMPARISON WITH SRTM
CONTINENT
MEAN
DIFF. (M)
STD DEV.
(M)
90% ABSOLUTE
ERROR (M)
AFRICA
1.3
3.8
6.0
AUSTRALIA
1.8
3.5
EURASIA
-0.7
3.7
6.6
N. AMERICA
0.1
4.0
6.5
S. AMERICA
1.7
4.1
7.5
NEW ZEALAND
1.4
5.9
10.0
24 Aug 05

15. RMS = 2.9 mgal in comparison with NGA’s “Best” Marine 5’x5’ File
KMS ’x2’g
KMS 2002 Dgs. Comparisons with these Dgs and NGA’s survey data with accuracies < 10 milligals were used to estimate these
RMS = 2.9 mgal in comparison with NGA’s “Best” Marine 5’x5’ File
24 Aug 05

16. GPS/Leveling Comparisons (±2 m edit threshold)
Weighted Mean Std. Deviation (cm)
Model (Nmax)
All
(10767)
NGS
(4649)
EGM96 (360)
PGM2004A (2159)
G99SSS (1’→10800)
PGM2005A (2159)
29.3
15.5 -
15.6
21.4
9.7
9.1
25.8
12.6
12.5
18.1
7.3
5.7
Linear Trend Removal
Before
After
24 Aug 05

17. GPS Leveling Comparisons over Some Areas with New g
Statistics before bias removal. 2 m edit applied.
Area (Npts)
PGM2004A
PGM2005A
Mean Diff.
(cm)
Std. Dev. (cm)
Tasmania (46)
Greece (36)
Japan (826)
Switzerland (115)
-25.2
-69.2
-22.0
-59.8
60.1
22.6
18.7
13.4
-20.2
-73.1
-21.1
-53.6
12.6 
17.5 
17.0 
28.5 ?
24 Aug 05

18. Upcoming EGM06 Activities
Spherical harmonic synthesis software will be made available at end of 2005
Official EGM06 project software
Provides ability to efficiently compute geodetic quantities to n=m=2160
Test sets to be provided
Available thru
Validation of new EGM06
GPS/leveling, orbits, DOVs, etc.
International participation is welcome
Spring 2005 timeframe leading to final EGM06 selection
24 Aug 05

19. Summary EGM06 is planned for June 2006
New surface and airborne gravity collected until Jan 06
Goal of EGM06 is 15 cm
n=m=2160
5’x5’ resolution
Latest GRACE model, Surface Gravity, Satellite Altimetry, SRTM and ICESAT data will be utilized
Error Propagation to n=m=2160
5’x5’ gravity data from unsurveyed areas
is welcome
24 Aug 05